Method for production of a photographic film

ABSTRACT

CONSISTENT SENSITOMETRY OF A BATCH OF PHOTOGRAPHIC FILM COMPRISING A PHOTOSENSITIVE EMULSION COATED ONTO A SUBSTRATE IS MAINTAINED BY SUNSTANTIALLY CONTINUOUSLY MELTING A MASS OF A GELLED PHOTOSENSITIVE EMULSION AT A RATE EQUIVALENT TO ITS DEPOSITION RATE UPON THE SUBSTRATE.

May 14, 1974 METHOD FOR PRODUCTION OF A PHOTOGRAPHIC FILM D. WANG Filed May 5, 1971 RESERVQlR ILLING AND 52 DRYING QTXLXIHQN COATING STATION FIG. I

INVENTOR. PEG DAVID WANG 0/!) KW W AT HORNE vs United States Patent O 3,810,778 METHOD FOR PRODUCTION OF A PHOTOGRAPHIC FILM David Wang, Lexington, Mass., assignor to Polaroid Corporation, Cambridge, Mass. Filed May 3, 1971, Ser. No. 139,598

Int. Cl. G03c 1/74 US. Cl. 117-34 5 Claims ABSTRACT OF THE DISCLOSURE Consistent sensitometry of a batch of photographic film comprising a photosensitive emulsion coated onto a substrate is maintained by substantially continuously melting a mass of a gelled photosensitive emulsion at a rate equivalent to its deposition rate upon the substrate.

BACKGROUND OF THE INVENTION The present invention relates to method and apparatus for the manufacture of photographic film. More specifically, the invention is concerned with the controlled melting of a portion of a mass of a gelled photosensitive emulsion and to the coating of the emulsion onto a substrate.

As is well known in the art, an initial step in the fabrication of photographic film is the manufacture of photosensitive emulsions which are capable of providing a developable image. The art is cognizant of the various steps employed in the production of such emulsions, which steps include chemical and spectral sensitization, ripening and after-ripening, etc. These procedures are well known and are thoroughly discussed in basic texts such as Mees, Theory of the Photographic process, Third Edition, MacMillan. Once the emulsion has been after-ripened and sensitized to a point where it produces the desired sensitometry, the emulsion is customarily chilled and stored in the gelled state. This highly sensitized form of emulsion is in a metastable state and it is necessary to prevent further ripening at this stage since the stable state which would be achieved by continual ripening is a totally 11 fogged, photographically useless material.

When a gelled emulsion is to be utilized in the production of photographic film, it is customary to melt all of the gel in a given batch. The resulting emulsion is thereafter coated onto a substrate employing any one of sevt er-al conventional coating techniques. After being coated on the substrate, the emulsion is chilled back to the gel state and dried.

This known procedure is subject to certain disadvantages. For example, because all of the gel is originally sensitometry which varies as a function of when a given increment of the emulsion was placed on the substrate. Consequently, the resulting photographic film has the disadvantage that it possesses different sensitometric characteristics along its length.

SUMMARY OF THE INVENTION It is a primary object of the present invention to obviate the aforementioned disadvantages of the prior art procedure by the provision of a system in which the photo sensitive emulsion is melted from the gelled configuration at a rate which is regulated by the rate of deposition of 3,810,778 Patented May 14, 1974 the emulsion onto the substrate. In this fashion, the length of time that each increment of emulsion is in the ungelled state between the time of its melting and its being chilled back to the gelled state after being coated on the substrate is maintained relatively constant in order to achieve uniform photographic film sensitometry.

The melting of the gelled emulsion at a rate consistent with its rate of use in the coating operation has the further advantage of preventing bacteria culturing and avoids needlessly melting all the gelled emulsion in a given batch when only a portion of the batch is to be utilized in a coating operation. Heretofore, in the event that a small amount of emulsion was to be removed from a large mass, the total mass of the gelled emulsion was melted and a small amount of the liquified emulsion was poured off thereby causing sensitometric changes and rendering the remaining material subject to bacterial infestations.

The coating system of the instant invention preferably includes at least two jacketed storage tanks which are disposed in parallel. A photosensitive emulsion having a given desired sensitometry, which may be determined by the technique described in US. Pat. No. 3,507,617, for example, a silver halide emulsion, is poured into the storage tanks, and the tanks are then chilled either by running a refrigerant through heat exchange coils disposed in or about the tanks, or by placing the storage tanks into a refrigerator in order to convert the emulsion into the gelled state. When it is desired to utilize either a small amount of emulsion or the entire gelled slug of emulsion in a film coating apparatus, a storage tank is positioned to feed into a coating applicator. A heating medium such as hot water is run through the coils within the tank in order to melt the lowermost portion of the gelled mass. Sufiicient heating medium is also run through the side jackets of the tank to provide a thin, slippery film of'emulsion between the chilled mass and the tank walls so that the mass will slide downwardly to impinge upon the hot coils in the bottom of the tank as the melted emulsionifiows out of the-discharge opening at the bottom on the tank.

The coating apparatus preferably includes an emulsion reservoir which is disposed between the storage tanks and the actual, coating applicator. When the supply of emulsion from one of the storage tanks to the reservoiris exhausted, control means automatically commence 'the feeding of emulsion from the second storage tank to the reservoir. In the context of the present invention, the reservoir should comprise the smallest volume suitable for the particular coating system.

The supply of heating fluid to the tank coils is regulated as a function of the amount of emulsion passed through the coating applicator so that the amount of emulsion melted corresponds to the amount of emulsion being consumed in the coating operation. I

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a diagrammatic view of a system for melting gelled emulsion and applying the resulting emulsion onto a substrate in accordance with a preferred embodiment of the invention; and

FIG. 2 is a partial elevational view on an enlarged scale of the right side storage tank of FIG. 1 showing the arrangement of a heat exchange coil atthe bottom of the tank.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to the drawings and more particularly to FIG. 1, the system comprises two storage tanks each generally designated by reference numeral 10. The storage tanks have heat exchange jackets 12 disposed at their lower ends, and additional separate heat exchange jackets 14 and 16 extending annularly around the periphery of the vertical walls of the tanks. A heat exchange fluid may be supplied to the lower jacket 12 via inlet 18 and may be removed through outlet 20. Similarly, a heat exchange fluid is supplied to and removed from the jackets 14 and 16 by inlets 22 and 24 and outlets 26 and 28.

As best seen in FIG. 2, a heat exchange coil 30 is disposed within each tank and is supported a slight distance above the curved bottom of the tank by a plurality of coil supports 32. The coil 30 has an inlet conduit 34 and an outlet conduit 36 both of which extend through fittings provided adjacent the bottom of vessel 10. The coil inlet conduit 34 may be connected via a valve 42 to either a hot heat exchange fluid, for example, hot water supplied through a line 38 or to a cold heat exchange fluid, for example, cold water supplied through a line 40.

The storage tanks 10 may be filled with a photosensitive emulsion having the desired sensitometry, for example, a silver halide gelatin emulsion, in any suitable fashion such as by opening hinged tank covers 44 and pouring the emulsion into the tanks. The emulsion within the tanks is then. chilled to the gelled state. This may be accomplished by passing a refrigerant, for example, cold water through line 40, valve 42, and inlet conduit 34 into the coil 30. Refrigerant may also be passed into one or more of the heat exchange jackets 12, 14 and 16. Alternatively, the entire tank 10 may be stored in a refrigerator in order to gel the emulsion. The gelled emulsion remains within the tanks 10 until it is needed for use in the production of photographic film.

When the sensitized emulsion is needed for the production of photographic film, hot water at a temperature of between about 40 to 60 C. is introduced into coil 30 via line 38, valve 42 and inlet conduit 34 in order to melt the bottom portion of the gel mass adjacent the coil 30. Melting of this portion of the gelled mass may also be assisted by introducing hot water into the lower jacket 12.

Hot water or other suitable heat exchange fluid is also introduced into the jackets 14 and 16 at this time. It is a feature of the invention that the amount of heat exchange fluid introduced into jackets 14 and 16 is carefully regulated to be suflicient only to transfer enough heat through the tank walls to melt the outermost surface of the gel mass in order to provide a thin, lubricating film of ungelled emulsion between the remainder of the gelled mass and the tank walls. This thin film of emulsion enables the gelled mass to slide downwardly and impinge upon the coil 30 as the lowermost portion of the gelled mass is melted and discharged from tank 10 through a valve 46 which may be a flush type sanitory plug valve into a discharge conduit 48.

The conduit 48 transports the photosensitive emulsion to an emulsion reservoir 50 from which the emulsion is passed on demand through a supply conduit 52 to a conventional coating station 54. At the coating station the emulsion is coated onto the upper surface of a substrate 56 to provide a photographic film comprising the substrate and an upper emulsion coating 58. The emulsion coating is then chilled to the gel state and dried conventionally at the schematically designated chilling and drying station 59.

In normal operation, emulsion will be melted and passed from only one of the tanks 10 to the reservoir 50 at any given time. When the flow of emulsion through conduit 48 from one of the tanks 10 stops, as may be indicated by sensors 64, suitable control means such as controller 60 opens the valve 46 at the bottom of the other tank 10 so that emulsion flows from this tank to the reservoir 50. It will also be appreciated that more sophisticated control means may be provided if desired including timing means to commence the melting of the gel in the standby tank just prior to the time that this tank will be put one stream by the controller 60. When the contents of a given ank have been exhausted, a reservoir supply function has been transferred to a parallel tank, the empty tank is replaced by a tank filled with gelled emulsion.

It is another feature of the invention that the amount of hot heat exchange medium supplied to coil 30 and, if desired, also to the lower jacket 12 may be regulated by a controller 62 in direct proportion to the flow of emulsion from reservoir 50 through supply conduit 52 to the coating station. In this fashion the amount of melted emulsion formed at the bottom of tank 10 may be regulated to substantially correspond to the amount of emulsion pass ing through supply conduit 52 to the coating station. Since the amount of emulsion melted in the tank 10 per unit time is substantially the same as that utilized during the same increment of time in the coating operation, greater uniformity in the time that various portions of emulsion from a "given gelled batch are in the ungelled state is achieved with a consequent improvement in the uniformity of the sensitometric characteristics of a photographic film comprising such emulsion.

It is presently preferred that as the level of the chilled mass falls within one of the vessels 10 due to removal of the melted emulsion, the removed material will be replaced by nitrogen pumped into the tank through inlet 70. The use of nitrogen rather than ambient air avoids contamination of the gelled emulsion within the tanks 10. It is also preferred that upon filling of the tanks with emulsion they be purged of ambient air with nitrogen.

The illustration in FIG. 1 is diagrammatic and it will, of course, be appreciated by those skilled in the heat exchange art that additional conventional control means will be employed to carry out the invention industrially. For example, the flow of heat exchange media may also be regulated by control means responsive to temperature sensing means which sense the temperature of the emulsion within the tanks 10 both adjacent the coils 30 and adjacent the heat exchange jackets. It will also be appreciated that conventional valves and fluid flow circuits may be employed to interchangeably pass hot or cold heat exchange media to the tank jackets. These circuits may also include provision to enable one heat exchange fluid to be drained from the jackets through the normal inlet conduit to the jackets prior to introduction of another heat exchange fluid into the jackets.

It will be further evident that the instant invention contemplates an emulsion blending functionality which may be accomplished, for example, by utilizing a multiplicity of the denoted storage and dispensing tankseach of which retains an emulsion which is to be blended with an emulsion of different constitution-in communication with a reservoir. In efiect, the reservior serves the function of a mixing vessel and may contain mixing means to assure proper blending. Precise proportionation may be obtained by using a control system as described hereinabove. Furthermore, for certain systems, even absent blending considerations, it may be desirable to use a mixing means such as an agitator in the reservoir.

While a presently preferred embodiment of the invention has been shown and described with particularity, it will be appreciated that various changes and modifications may readily suggest themselves to those of ordinary skill in the art upon being apprised of the present disclosure. For example, the description of the preferred embodiment of the present invention depicts heat transfer means which comprise water jackets and coils. It is naturally contemplated that any other suitable heat transfer means, such as electrical means, etc., may be utilized in their stead. It is intended that any changes and modifications which fall within the scope and spirit of the appended claims are encompassed thereby.

What is claimed is:

1. In a method for the production of a photographic film wherein a liquid photosensitive emulsion is coated onto a substrate at a coating station and the coated emul sion is thereafter transformed to the gel state and dried, the improvement comprising controlling the How of emulsion to the coating station by the steps comprising: isolating a mass of gel of the emulsion from the ambient environment by enclosing it within a storage and dispensing tank; melting the lower portion of the mass of the gel of the emulsion within the storage and dispensing tank; withdrawing the melted emulsion through a discharge opening of the storage tank; applying sufficient heat around the periphery of the storage tank to melt the side surface of the gel mass to form a lubricating film of melted emulsion on the inner wall of the storage tank whereby upon discharge of the melted emulsion the remaining gel progressively moves by gravity towards the lower end of the tank for eventual melting and discharge through said discharge opening; and passing the withdrawn emulsion to the coating station.

2. A method according to claim 1. wherein said discharge opening is in the bottom of said tank.

3. A method according to claim 4 further comprising controlling the amount of heat supplied to melt the gel as a function of the desired rate of flow of melted emulsion through said discharge opening.

4. A method according to claim 2 further comprising providing a plurality of storage and dispensing tanks containing gelled emulsion; connecting the discharge openings of the storage tanks to a reservoir which supplies emulsion to the coating station; passing emulsion from only one of said storage tanks to the reservoir; and upon the cessation of flow from said one storage tank to the reservoir commencing the flow of emulsion from another storage tank to said reservoir.

References Cited UNITED STATES PATENTS 3,395,034 7/ 1968 Przybilla 117-34 3,431,890 3/ 1969 Uluary 117-37 3,079,272 2/1963 Greig 117-37 2,790,728 4/ 1957 Foster 117-34 3,133,484 11/1967 Wright 117-37 2,157,286 5/1939 Emmey 117-37 LE OTHER REFERENCES Making and Coating Photographic Emulsions, by Zelikman et a1., Emulsions Coating, pp. 21 to 24.

WILLIAM D. MARTIN, Primary Examiner W. R. TRENOR, Assistant Examiner US. Cl. X.R. 

